The present invention relates to a security paper and more particularly to a security paper used in particular for the manufacture of banknotes, passports, certificates of authenticity and checks.
The invention also relates to a process for manufacturing said security paper.
Very many printed documents require increasing means for ensuring their authentication and their security protection.
These documents range from banknotes to travel documents, and also include scratchcards, playing cards, checks, identity cards and passports.
To allow the user or holder of the security document to check the authenticity of the document in a simple and reliable manner, it is common practice to include authentication elements within the thickness of the constituent material of the document.
Under certain specific conditions, these elements emit signals that can be detected, generally with the eye, the observation of said signals revealing the presence of said elements within the document and, consequently, guaranteeing its authenticity.
The inclusion of such elements is also designed to prevent malintentioned persons from counterfeiting said document by reproducing, identically or almost identically, the characteristics of said document.
The suppliers of security documents, aware of an increase in the level of expertise and organization of potential counterfeiters in this field, have in recent years envisaged increasing the number and variety of the authentication elements present within any one security document.
The solutions envisaged in this regard do however have certain problems.
Firstly, the possibility of reproducing, identically or almost identically, the security document is not fundamentally reduced owing to these further additions of security elements.
A counterfeiter, sufficiently patient and correctly equipped, is in fact capable of discovering the nature and the exact quantity of the elements constituting the document to be counterfeited.
By reproducing the steps for obtaining the document, which steps have not been modified, it is not impossible to end up with an almost perfect reproduction of the document in question.
Secondly, it may turn out that this solution does not actually meet the requirements of users in this field.
In fact, the customary user rarely checks all of the security elements present in a given document.
Only the most easily and directly detectable elements are checked by him.
In the case of a banknote for example, these are generally the watermark or certain colored fibers or iridescent particles visible to the naked eye.
Lastly, the presence of an increasing number of security protection elements within the same base structure may result in impediments between security protection elements having mutually incompatible physical properties.
Thus, in the case of banknotes, it is sometimes necessary to opacify the fibrous material so as to increase the rendition and contrast of the watermark.
This opacification may then make it harder to see the other particles or fibers intended for authentication.
Only the particles or fibers located on the surface of the banknote will be visible, the others being embedded in the opaque fibrous layer.
U.S. Pat. No. 5,565,276 describes a security paper that can be formed from a first ply of paper and from a second ply with a smaller weight than that of the first ply and containing iridescent planchettes as authentication element. The object of that patent is to improve the visibility of the planchettes.
However, it remains necessary to further improve the security protection of security documents and/or their mechanical strength.